Traffic detector



J L. BARKER 2,441,554

TRAFFIC DETECTOR Filed may 18, 1944 May 18, 1948.

2 Sheets-Sheet 1 AM w, 111%.0 -RM M y 8, 1948. mm zm 9 5 TRAFFIG DETECTOR Filed. may 18,, 1.53443 2 Simets-Sheei 2 mum in Patented May 18, 1948 'mAmc nnmc'roa John L. Barker, Norwallr, Conn. asslgnor to Eastern Industries, Incorporated, a corporation of Delaware Application May 18, 1944, Serial No. 536,129

14 Claims. (01. 171-209) This invention relates to an improved traffic detector, and particularly to a trafiic detector utilizing the generative eilect of disturbed magnetic fields, to actuate counting means, signal or warning means, traffic control systems, conveyor systems, and the like.

It is an object of the invention to provide an improved device of the magnetic type which may be disposed in or adjacent a path or channel over which vehicles, packages, or other bodies are moving, to detect such bodies as contain magnetic metal, and to employ the inductive efiect of the passage thereof through a magnetic field to induce a voltage which may be employed in any desired manner in a suitable electric circuit.

It is another object of the invention to provide an improved magnetically actuated detector in which coils are disposed about relatively vertically positioned para-magnetic cores which are not pre-magnetized, but serve to direct or channel the vertical component of the earths magnetic field.

It is a further object of the invention to provide a magnetic detector which is compensated against the disturbing effect of extraneousmagnetic impulses such as created by power lines and other field-generated structures in the locality, but will be directionally sensitive to traiiic now within the relatively sharply defined field of the detector.

It is still another object of the invention to provide a trafiic detector of the induced voltage generation type, which is non-critical as respects coil windings, and the type and disposition of the cores of magnetic material therefor.

it is another object of the invention provide I traffic detector which may be permanently rim bedded in the concrete or'other material of a roadway, and does not require moving parts or pressure-actuated mechanisms for traiiic detection.

It is another object of the invention to provide improved magnetic detection means which will difierentiate between trafilc moving in a plurality of directions, and will actuate detection, signailing, or control means only for Lafllc flowing in a predetermined direction.

It is an object of the invention to providea.

2 operation of the trafllc control or other system and thus to insure that only traflic passing in the opposite direction will be detected.

Induced voltage devices for the detection of masses of magnetic material, are known in the art, and utilize the phenomenon that a body of magnetic metal which cuts lines of magnetic force will induce a voltage in a coil disposedin the magnetic field.

The present invention contemplates the employment of a suitable plurality of bars of magnetic material-cold rolled steel bars perform satisfactorilyarranged in suitable spaced relationship in a preferably quadrilateral iramelike structure, and disposed vertically, to provide channels through which pass the vertical component of lines of force of the earth's magnetism. Disposed about each said bar, is a coil of wire; a

set of coils which are in the same line of position transversely of the movement of traflic are connected in parallel, and the parallel-connected coils of a set disposed therefrom in spaced relationship in the direction of trafiic flow, have a reversed winding as compared with said firstnamed set.

Through each of the coils of each set, therefore, flow lines of force of the earths magnetic field; and when the flux through each said cell is disturbed, as by movement of a magnetic body through the flux pattern, an E. M. F. having a characteristic voltage wave, is induced in the coils. Because of the relative reversal of wind ing each set'of coils, the voltage induced is of opposite polarity.

By pro-establishing the capacity value of the circuit for each set of coils so that the total pacity of one set is higher than the total capacity of the second set, the voltage effect of the first set may he delayed. Assuming that it is desired not to detect trafic flowing in such direc tion as to pass sequentially over the first and second coil sets, the delayed voltage may be superposed upon the voltage induced in the second coil units. By reason of the opposite-polarity characteristic of the respective induced voltages, the said voltages substantially nullify each other, and are ineffective to operate the signalling or other detection means.

Features of the invention are that the detector is accurately directionally selective over a wide range of traffic speeds and has a relatively sharp- 1y defined area of operation. An additional feature resides in its inherent compensation against extraneous field-generating influences.

In the following detailed description, the in- 3 vention has been illustrated with respect to its application to the detection of vehicular highway traffic, but it will be readily apparent to those skilled in the art that many other applications are within the scope of use of the invention.

In the accompanying drawings, which illustrate one practical embodiment of the invention:

Fig. 1 represents a trafilc intersection, one street of which has detectors embodying the present invention; a trafiic signal and a control for operating the same upon passage of vehicles across the respective detectors in the direction of the intersection, are schematically shown;

Fig. 2 is a diagrammatic representation of a detector disposed beneath the surface of the roadway, and looking in the direction of the arrows 2-! of Fig. 1;

Fig. 3 is a plan view of apparatus embodying the present invention;

Fig. 4 is an end elevation of the same on lines 4-4 of Fig. 3;

Fig. 5 is a vertical sectional detail on lines 0-5 of Fig. 3, illustrating a coil and junction box for the electrical connections therefrom;

Fig. 6 is a wiring diagram showing the coil units and delay network;

Fig. 'l is a typical amplifier circuit; and Fig. 8 is a diagrammatic representation of induced voltage curves, for the purposeof illustrating the objectives of superposition of induced voltages for one direction of traffic flow. and separation of voltages for trafiic flow in the opposite direction.

Referring to the drawings, one practical embodiment of the magnetic detector D includes preferably rectangular frames III. II, joined and maintained in suitably spaced relationship, by pairs of bars or rods I 2 secured thereto. Said rods serve as cores for the voltage-generator coils, arranged in sets or pairs, and designated ll, 0 and I5, I50, respectively. Rods-l2 are of magnetic material; in the present invention, cold-rolled steel is substantially as effective as the high-permeability steel alloys such as Allegheny-Ludlum 4750.

For vehicular trafllc control, each said frame may be 48 inches by 12 inches, and spaced 9 inches apart by the rods II. The longer sides of each frame, which are disposed transversely of the direction of traffic fiow, are preferably standard rolled steel structural shapes I6, I! such as angle or channel iron. Each frame is completed by end pieces i8, of brass or other nonmagnetic material, suitably secured as by the nuts and bolts illustrated. Brazing may be employed supplemental to, or in lieu of, the nut and bolt fastenings.

At one end of the structure, there may be supported, as by non-magnetic straps ID, a connection head 20, as later more fully described.

The rods I! are preferably disposed symmetrically on the frame. For a 48" frame the rods may be placed 12 inches from each end of the frame, there being two rods and coil assemblies on each of the pairs of frame members l8, l1.

Each of the coils consists of a large number, for example 20,000, of turns of #40 insulated wire wound on a /2" core. Such a. coil may be wound for housing within a non-magnetic casing 2| fixedly secured to each rod l2. The casings II are impervious to water or dampness; if desired, the casings may be filled with pitch, wax, or other water-repellent material.

Each coil is uniform as to its electrical characteristics. The electrical values of the coils are related principally to the strength of impulse generated therein, and to local stray or leakage current conditions, as is well known to those skilled in the art. Higher voltage output is obtained by increasing the number of turns, and such output is primarily adapted to the electronic amplifier as an impulse responsive device.

The rods 82, being paramagnetic, are conductors for the vertical component of the earth's magnetic force, and the local field of the earth's magnetism passes downwardly through the coils disposed about the rods. The magnetic frame elements l8 and I1 effectively enlarge the pole areas of the rods l2 associated therewith, in that the vertical magnetic field between and at the respective sides of the coils flow along said frame elements, thence into and downwardlythrough the respective rods I! for dissipation into the earth.

The respective sets of coils I4, I40 and I5. I50 are connected in parallel. as shown in Fig. 6. As is apparent from the circuit diagram, the direction of winding of one set of coils is the reverse of that of the other set, and therefore the voltage waves induced in the sets are of opposite polarity.

Leads from the respective coil sets are brought into the connection head 20, which may comprise a suitable threaded brass sleeve provided with a gland 22 through which the leads 2' pass to the control box C.

In a detector of four foot width, it has been found that it is most satisfactory to employ two coils in each of the voltage-generation units. The two coils, being connected in parallel, operate as a single generator.

Tests have established that the present detector reacts to the passage of magnetic metal in a path within six inches of either end frame member IS. The steel wheels of present day automobiles eiIectively induce a voltage in the coil units when passing through the magnetic field thereof, and the units are disposed in the roadway to take maximum advantage of conventional automobile tread.

For example, the unit D nearest the curb will, unless local tramc conditions dictate otherwise, be placed about six feet from the curb. Since the passage of a vehicle within six inches of the side of the unit remote from the curb is effective to generate an induced voltage, there is an effective operating area up to about five and one-half feet beyond the four foot width of the unit itself. Accordingly, one unit is effective over a fifteen foot trafilc lane. For wider lanes, a plurality of units D may be connected in series addition.

The units are installed in the roadway by excavating a suitable depression, temporarily supporting the unit therein, and completely filling the excavation with the road material. The units are not critical, and need not be accurately leveled, as must units in which the magnetic field is essentially transverse, rather. than vertical.

It is, of course, recognized that an automobile bodyin fact any metallic structure-is not magnetically homogeneous and the thereby induced wave form is not uniform or regular. A resultant action is present in each vehicle regardless of its heterogeneous magnetic condition. Therefore, the effect of the vehicle on two similar detector coils, will be similar.

For simplicity of demonstration of the induced voltage curves of the respective sets of coils, Fig. 8 shows a theoretical voltage curve obtained by the passage of a theoretically homogeneous magnetic structure successively over the sets of coils. Assuming movement of the imaginary magnetically homogeneous body initially across coils I4, M0, the voltage induced in said coils builds up as it approaches the effective axis of the coils, attaining a maximum value in plus direction immediately in advance of passing over said axis, then sharply declining to zero at the instant of passing, and building up to an equal negative value before again tapering off to zero as the magnetic body recedes.

Substantially the same voltage curve derives as the body approaches, passes over, and recedes from the coils-i5, I50; however, the reverse winding of said coils results in reversed polarity.

The reversed windings, and resultant reversed polarity of the induced voltages, operate as compensating means to preclude operations of the trafilc control system by the magnetic field efiect of such structures as overhead trolley or power lines, subsoil conductors or thelike, which usually parallel the roadway, and hence extend across the detector and simultaneously subject each coil unit thereof to a magnetic field.

To produce apparatus which is directionally selective over a wide range of vehicle speeds, and

resultant range of frequencies of the induced current, I include in the circuit, see Fig. 6, an electrical network which will introduce a substantially uniform space delay at all frequencies. The network increases the total capacity of the coil unit which is first to receive the impulse from traflic moving in the direction which is not to be detected. The network delays the induced voltage after the passage of the vehicle over the coil unit, and substantially superposes the said voltage on the approximately equal but oppositely polar voltage subsequently induced in the second coil unit, for'trafiic moving and the direction of the TRAFFIC DIRECTION" arrow as shown in Fig. 8. Hence, there is a substantial cancellation of voltage and resultant non-operation of the control or other apparatus in the circuit with the detector for trafllc moving in such direction.

.Assuming trafiic in the opposite direction (i. e.. opposite to the (TRAFFIC DIRECTION arrow in Fig. 8), the delay network distinguishes rather than superposes, the induced voltages, and either or both of the voltages generated may be employed to actuate the control or other apparatus. The respective sets of coils i4, I and i5, I are interconnected'in a three-wire circuit, including conductors 30. 3| and 32, the latter being common to the respective coils and the delay network, see Fig. 6. Condensers 33, 34 preload the circuit to compensate for possible variations in cable length, and resistances 35, 36 introduce a resistance preload in the respective circuits. Said resistances are conveniently of 4000 ohms each..

Resistances 31, 38 of 400 ohms each serve in combination with the resistances 40, 42 and M, 43, respectively, as voltage divider means. Typical values are 10 and 500 ohms respectively for resistances 40 and 42, and 100 and 5000 ohms, respectively, for resistances 4i and 43.

A condenser 44, of large capacity, say 40 mfd.,

is in series with resistor 40, and is opposed by condenser 45 of 8 mfd., in series with resistor 4|. Similarly, condenser 46, of 8 mfd. is across leg 30, 32, and condenser 41, of .1 mfd., is across leg 32, 3|.

It will be understood that the stated 'values of the respective electrical elements are subject to change in the field. Local conditions affect the 6 voltage generation, circuit capacity, etc., and may not accurately be ioretold.

As is apparent, the respective circuits 3!], 32 and H, 32 are unbalanced, and the former has substantially greater capacitance. Voltage generated in the former circuit will therefore be delayed as respects generation in the latter; and the result of the unbalanced capacitance is to superpose the respective induced voltages as aforesaid.

The extent of unbalance, however, is not so great as to result in widely variant voltage output of the respective coil sets.

Condenser as, being of relatively large capacity, is primarily eiTective for lowv traffic speeds, such as not in excess of 25 M, P. H., whereas at higher speeds, it is desirable to have a greater ratio between the opposed condensers in the respective legs, as evidenced by the relationship of 8 mfd. in' condenser 46, as opposed to .l mfd. in condenser er.

Experimental tests over a wide range of vehicuiar speeds indicate that the combinatio oi the condensers i l, 45, in opposition to condensers 45, 41, affords a correct space delay whereby at any Speeds from 3 M. P. H. to 60 M. P. H., the induced voltages are superposed for tramc passing initially over the coil I4, I40.

A typical amplifier circuit is shown in Fig, 7, it being understood that multi-stage amplification may be employed if necessary or desirable.

The impulse from conductors 30, 3t is impressed across the grid of tube at. For trafilc passing in a direction which is not to be detected, the small impulse from said conductors, by reason of the substantial nullification of the induced voltages, is insufficient to reduce the negative grid bias normally supplied from source 55, and there is insufficient output from the tube. as to energize and operate circuit closing relay 52, the output leads of which serve the t-raflic control S or other associated apparatus.

For vehicles passing in the opposite direction, however, there are two distinct voltages impressed on the negative grid bias, and the positive components of such induced voltages reduce the negative grid bias. to increase the plate current of the tube 50, and hence actuate the relay to close the output circuit thereof.

Galvanometer relays, or other relays of a polarized type may be employed in lieu of the illustrated amplifier and relay. However, the sturdier construction and dependability of the thermionic amplifier makes it generally more satisfactory over long periods of operation.

Whereas it is obvious that among the several objects of the invention as specifically afore noted are achieved. it is apparent that numerous changes in construction and rearrangements-of the parts might be resorted to without departing from the spirit of the invention as defined by the claims.

I claim:

1. In a direction selective trafiic detection apparatus having an electric output device to be actuated only by bodies containing magnetic material passing in a selected one of two permissible directions of traffic along a trafiic artery, the combination of two voltage-generation coils having magnetic fields passing therethrough, said coils being spaced sequentially along said artery in the path of traffic flow, whereupon the passage of said magnetic bodies sequentially through the field of each coil induces a voltage therein, an electric circuit interconnecting said coils in series opposition for reversing the polarity of voltage seneration in one coil with respect to the other, an output circuit from said coils, a work circuit connected to the respective output circuits of said coils for transmitting generated voltage to said output device; and a delay network includinga plurality of capacitors or successively less capacitance individually connected across the output circuit of each of said coils, the capacitors of one said output circuit being respectively less than the correspondingly positioned capacitors or the other of said output circuits, whereby the voltage generation in the coil having the higher capacitance is delayed for substantial coincidence with the subsequently generated and oppositely polar voltage induced in the other coil for tramc flowing in one direction to result in substantially zero voltage in the work circuit and the successively generated voltages are individually apparent in the work circuit for trafllc flowing in the opposite direction.

2. In a direction selective trafllc detection apparatus having an electric output device to be 1. of traillc now, means for passing a magnetic field through said coils, whereupon the passage of said magnetic material sequentially through the field of each coil induces a voltage therein, conducting means interconnecting said coils in series opposition for reversing the polarity of voltage generation in one coil with respect to the other, an output circuit from said coils; a work circuit connected to the respective output circuits for transmitting the voltage generated by said coils to said output device; and a delay network including a relatively high-value capacitor across the output circuit of one of said coils, and a lesser-value capacitor across the output circuit 01' the other of said coils, whereby the voltage generation in the coil having the higher capacitance is delayed for substantial coincidence with the subsequently generated and oppositely polar voltage induced in the other coil for trafiic flowing in one direction to effect substantially zero net voltage in said work circuit and is separate therefrom and is thereby apparent as individual voltage pulses in the work circuit for trailic flowing in the opposite direction.

3. In a traiilc detector of the magnetic type adapted to'be located adjacent to a path of traillc how and including voltage actuated means for directionally detecting the passage of magnetic units of trailfic in such path, the combination oi two voltage-generation coils spaced sequentially along said path, paramagnetic cores in each of said coils for directing the vertical component of the earths magnetic field thereto said voltage actuated means; and an electrical network in circuit with at least one of said coils and embodying capacitors to delay the voltage generation thereof for substantial coincidence with the voltage generated in the second of said coils for trailic flowing in one direction to substantially nullify the respectively generated voltages, and to distinguish the respectively generated voltages for trafllc flowing in the opposite direction whereby said voltage actuated means will not be operated upon traillc flow in the said one direction.

4. A device for the detection of magnetic bodies traversing a predetermined tramc path, comprising voltage generator means including cores of magnetic material disposed in spaced relationship along the path of trafllc flow and a coil of wire disposed about each said core, whereby passage of magnetic metal sequentially through the fields of the respective generator 'means induces distinct voltages therein; conductor means interconnecting said coils in series opposition, and ailording a conductor from each coil for external connection; an electrical network in circuit with said conductors and including means whereby the capacity of the output circuit oi. one of said voltage generating means is greater than that of the second of said voltage generating means to delay the voltage generation in the first-named generator for substantial superposition upon the voltage generation oi? the second said generator to substantially nullify the output of the respective generators for trafllc flow sequentially across the generators in one direction and to distinguish the voltages upon trafiic flow in the opposite direction.

5. A device for the detection o1 magnetic bodies traversing a predetermined trafiic path, comprising electromagnetic generators including a magnetically permeable core and coil unit disposed inspaced relationship along said traiiic path and arranged for induced-voltage generation 1 each said electromagnetic means upon passag of a magnetic body successively within the magnetic field of each said generator; an electric circuit interconnecting said generators in series opposition, whereby the voltage generated in each said means is of reversed polarity; combined capacitance and resistance means in circuit with one of said generators to delay the voltage generation therein, whereby to impose the said voltage upon the reversed-polarity voltage oi! the second of said generators for trailic flowing in one direction and to distinguish the respectively generated voltages for trafllc flow in another direction.

6. A device for the detection oi. magnetic bodies traversing a trafilc path, comprising an organization of paramagnetic cores disposed vertically and in spaced relationship in line transversely to flow of traffic; 8. voltage-generation coil about each of said cores, said coils being interconnected in parallel; a second organi zation of paramagnetic cores and parallel connected coils thereon disposed vertically and in spaced relationship transversely of trafllc flow, said two organizations being mutually spaced in the direction of trafllc flow; means for connecting the respective coil organizations in series opposition and affording output conductors for the respective organizations from such series opposition connection.

7. In a direction-responsive trai'fic detector the combination of a coil of wire disposed be neath the path of trailic flow; a second, similarly disposed coil of wire spaced from the first coil in the direction of traffic flow; a. paramagnetic core within each said coil and extending vertically with respect to said trafllc path to conduct lines of force of the earth's magnetism through the said coils, whereby passage of magnetic metal above said coils induces a voltage therein; means for reversing the'polarity of the sa d induced voltage of one coil with respect to the other; and means for delaying the generation of voltage in one coil proportionally to the speed of passage of said magnetic metal to superpose the respectively induced voltages for trailic flowing in one direction and for separating the said voltages for traffic flow in the opposite direction.

8. A compensated traiiic detector apparatus, comprising a pair of substantially identical detecting elements each comprising a magnetically permeable core and a coil thereon, said cores being disposed substantially vertically for subjection to the vertical component of the earth's magnetic field and arranged in spaced relationship in the direction of traffic flow in a trafilc path, conductors interconnecting the coils of said detecting elements in series in electrically opposing relationship with respect to voltages induced therein by variations in the magnetic field within each said coil and providing output leads from such series connection.

9. A voltage-generation unit for a traffic detection device, comprising relatively long, rigid members of magnetic material arranged transversely to a traffic path, relatively short spacers of magnetic material for disposing the said members in vertically spaced relationship beneath such traffic path and said spacers being themselves spaced transversely to such path, and coil means disposed about each of said spacers and electrically interconnected in parallel.

10. A voltage-generation unit for a trafiic detection device, including an elongate frame having structures of magnetic material extending transversely of the path of trailic flow and maintalned in fixed spaced relationship in the direction of traffic flow by non-magnetic meansya paramagnetic core extending substantially vertically from each of said magnetic structures, and a coil of wire disposed about each of said cores, the windings of the respective coils being connected in series opposition relatively to each other.

11. A voltage generation unit for a trafllc detectlon device, comprising a relatively long, rigid structure of magnetic material disposed transversely of the path of traffic flow; spaced paramagnetic core means secured to said structure and extending substantially vertically downwardly therefrom; and coil means disposed about each said core means and electrically interconnected in parallel.

12. A voltage-generation unit for a traific detection device, adapted to be disposed across a trafllc path, comprising relatively long rigid members of magnetic material, spacers of magnetlc material for disposing the said members in vertically spaced substantially parallel relationship and said spacers being relatively short compared to said members and being spaced in substantially parallel relationship. along said members and substantially perpendicular thereto and coil means disposed about each of said spacers and electrically inter-connected in parallel.

13. A voltage-generation unit for a tramc detection device adapted to be disposed across a trafllc path, comprising a framework of relatively long rigid members of magnetic material adapted to be disposed transversely to a traffic path and spacers of magnetic material disposing the said members in vertically spaced substantially horizontal planes and said spacers being relatively short compared to said members and being spaced alongsaid members in substantially perpendicular relation to such planes, and coil means disposed about each of said spacers and electrically connected in parallel for generation of voltage in such coil means upon passage of traflic containing magnetic material across said framework, another framework and associated coil means similar to the first mentioned framework and coil means, means of substantially non-magnetic material spacing the two frameworks in substantially parallel vertical planes; and means connecting the coil group of one framework in series opposition with the coil group of the other framework.

14. A trafllc detector device including a framework of relatively long rigid members of magnetic material adapted to be disposed transversely to a traffic path and spacers of magnetic material disposing the said members in vertically spaced substantially horizontal planes and said spacers being relatively short compared to said members and being spaced along said members in substantially perpendicular relation to such planes, and coil means disposed about each of said spacers and electrically connected in parallel for generation of voltage in such coil means upon passage of traffic containing magnetic material across said framework, another framework and associated coil means similar to the first mentioned framework and coil means, means of substantially non-magnetic material spacing the two frameworks in substantially parallel vertical planes; and means connecting the coil group of one framework in series opposition with the coil group of the other framework, and means delaying generation of voltage in the coil group of one framework for substantial superposition and neutralization of voltages for traffic in one direction and for separation of voltages for detection of traiiic in the opposite direction.

JOHN L. BARKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,062,361 Ryder May 20, 1913 1,992,214 Katz Feb. 26, 1935 2,014,410 Pierce Sept. 17, 1935 2,064,882 Brainerd Dec. 22, 1936 2,119,811 Green June 7, 1938 2,166,090 {Cooper July 11, 1939 2,201,146 Barker May 21, 1940 FOREIGN PATENTS Number Country Date 201,126 Switzerland Feb. 1, 1939 

